Montana bangs case caught by routine testing
The Montana Department of Livestock (MDOL) reported last week that a suspected case of brucellosis in Park County has been confirmed. Six bred heifers from a 150-head herd were determined to have reacted positive to initial screening tests in mid- September. Cultures performed at the National Veterinary Services Laboratory in Ames, IA, on a milk sample collected at the time have confirmed the presence of brucellosis.
Park County, along with portions of Gallatin, Madison and Beaverhead counties, make up Montana’s “Designated Surveillance Area,” or DSA, which has special testing regulations in place to control the spread of brucellosis due to the region’s proximity to Yellowstone National Park. Ac cording to USDA’s Animal and Plant Health Inspection Service (APHIS), elk and bison in the Greater Yellowstone Area represent the nation’s last remaining natural reservoir of brucellosis. Despite ranchers’ efforts to eradicate the disease in their herds, transmission from wildlife to cattle in this region has been an ongoing issue. But since better science has prompted USDA to revise its handling of brucellosis cases, infections like the one in Park County are no longer as devastating to local ranchers.
Until recently, two or more cases of brucellosis within a twoyear period in a given state was almost certain to lead to the state’s losing its “brucellosis-free status.” Losing this prized classification could result in costly restrictions on interstate cattle shipping, as well as the infected herd being depopulated, typically wiping out the rancher.
However, improved surveillance methods and vaccines have caused APHIS to relax the laws somewhat. Although Montana had back-to-back bangs cases in cattle in 2007 and 2008, and in a bison
herd in 2010, there is no expectation that the latest Park County case will result in any major disruption of cattle shipping as it would have under the old regulations. And while the six infected cattle were slaughtered on Sept. 22 and the herd has been quarantined while the rest of the cattle are being tested, according to Steve Merritt, MDOL public information officer, there are no plans to depopulate the entire herd. Merritt indicated that ranchers in the surrounding area will be carrying on “business as usual.”
Indeed, the fact that the infection was detected before the infected cattle were sold or shipped is being hailed as proof that existing security measures are effective. “As unfortunate as it is that there was a transmission to livestock,” said Marty Zaluski, Montana state veterinarian, “the fact remains that we found … those animals in the state of Montana, in the DSA before they were exported out of state.”
Enhanced surveillance for cattle within the DSA has been in place since 2008. All sexually intact cattle over 12 months leaving the area or otherwise being sold must be tested. Montana also requires that all cattle in the DSA be vaccinated against the disease. There is, however, no state-wide vaccination requirement.
Brucellosis is a highly infectious and costly bacterial disease that can be carried by cattle, bison, elk, deer, goats and sheep, as well as pigs and dogs. The disease can also be transmitted to humans as undulant fever, a flu-like illness that can become chronic. In cattle, the disease results in abortions, infertility and reduced milk production.
The expectation is that the recent infections in Park County are the result of cross-species infection from elk, although this has not yet been confirmed.
“We are strongly suspicious that elk are the source of this latest infection,” said Zaluski. “Brucella has been well-documented in local elk herds. We are not familiar with any additional cattle herds that have brucellosis in the area, and we don’t believe that infected bison were in the area.”
How to manage transmission of brucellosis from free-roaming herds of elk and bison has been a fraught issue. Some attempts at controlling the disease have involved testing and slaughtering infected wildlife. And while the livestock industry has supported management actions, environmental groups have largely opposed them. Earlier this year, Western Watersheds Project and several other non-profits filed suit against federal plans to cull a herd of 400 Yellowstone Park bison that were suspected of carrying the disease.
Zaluski explained that addressing the endemic brucellosis issue in the Greater Yellowstone Area will require a multi-pronged approach that recognizes several factors that are contributing to the problem: first, that brucellosis exists at a high rate in elk feed grounds in Wyoming; second, that brucellosis exists in a very high percentage of Yellowstone Park bison; and third, that large populations of elk congregate during the high-risk times of the year where the disease can be passed from one elk to another.
“I suggest that we need to have stronger actions on all of those fronts,” said Zaluski.
That the six infected cattle had been vaccinated for brucellosis underlines the fact that vaccination is not by itself an answer to keeping brucellosis out of livestock.
“When folks in the conservation community say, ‘Well, you just need to vaccinate your cattle and then it won’t be a problem,’” remarked Zaluski, “that is not, in fact, the fix-all solution that they would like to have you believe.”
Although the brucellosis vaccination helps to prevent the disease, like any vaccine, it provides no iron-clad guarantee of immunity. However, in the event that an animal does contract the disease, if it has been vaccinated it will still mount an immune response that will likely prevent the disease from progressing to the point of causing the animal to abort. Five of the six heifers that were diagnosed did not abort, while it is unclear whether the remaining heifer was bred.
“The vaccine is most effective at preventing abortion, and therefore [preventing] spreading disease to other animals in the herd,” said Zaluski. “It is not as effective at preventing the infection from happening in the first place. So, the vaccine did what it was supposed to do, to a large degree.”
By contrast, when unvaccinated cattle contract brucellosis, the disease quickly progresses to cause abortion. Aborted tissues and blood are highly infectious. Curious cows sniffing at aborted calves can easily get the infection, and the disease can spread through a herd like wildfire.
“The abortion is a very efficient way to transmit the brucellosis,” Zaluski explains. “That’s really the number one way that brucellosis is transmitted. …[Abortions] would result in a much higher number of animals in any given herd getting infected, and it would also … create additional risk for neighboring cattle herds contracting the disease.”
Until and unless brucellosis is eradicated in wildlife populations, it is likely that ranchers in the Greater Yellowstone Area will have to face sporadic cases within their livestock. Yet Zaluski remains optimistic that the increased security in the region will ensure containment of the disease without overburdening the livestock industry across the state.
“We hate to see it happen, but it shows that the state’s Designated Surveillance Area is working as intended,” Zaluski stated in a press release. “These animals were tested per DSA requirements, and the disease was found before the animals were moved. Other states can remain confident we’ll find the disease, should it occur, before it leaves the state.”